Rear windows

Guys i need fast help. I am in Billing now, and will be leaving tomorrow for London. I need to find rear windows (sliding ones) for our Defender 110, as these ones leak. Could any of you tell me where i could find them, as i only have two days, tomorrow and the day after, to roam through London in search of the windows. Any ideas of a shop or place where i can buy them, new exclusively?
Cheers.

My rear windows leaked and I found the bottom of the frame was bent. I straightened it out and they are now nearly water tight.